Ha, at using W-Summon KOTR + mime :P against Emerald. That's so spamming xD
My Strategy is using W-Magic + Demi3 with all characters and using White Wind to restore your characters, that way you'll have at most 4 materias on your characters and his Aire Tam Storm attack will hit you for only 4444 HP.
For Ruby, start the battle with two downed characters, and start using Dazers on Ruby.
I suggest stacking up on Dazers, 99 of them. Dazers will paralyze Ruby for a long time, that way you can revive your other characters, and with ribbon or Status Effect - Hades on your armor slots, you'll be protected against most status effects from the tentacles.
Just keep using Dazers and your attacks plus the limit breaks which will build up during the battle.
Never, and i stress this, NEVER, use KOTR on him, he'll just counter with a 9000-9999 damage Ultima.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
